1. Field of the Invention
The present invention relates to a muffler of an internal, combustion engine used for a vehicle such as a motorcycle and an automobile.
2. Description of the Related Art
Conventionally, in a vehicle such as a motorcycle and an automobile, exhaust as from an internal combustion engine is discharged to the rear of the vehicle via a muffler. The above-described muffler usually has a muffler main body forming one or a plurality of sound-deadening chamber(s) and a tail pipe extended from a rear end surface of the muffler main body. Thus, it is so constituted that the exhaust gas from the inner combustion engine passes through the noise-deadening chamber of the muffler main body and thereafter the exhaust gas is discharged from the tail pipe.
In the muffler of the above constitution, exposing the tail pipe from the rear end surface of the muffler main body is not preferable in terms of design of the vehicle. Thus, a tail cover is integrally formed with the muffler main body, in a manner to cover an outer periphery of the tail pipe. Further, there is formed a ring-like gap in which a tube is to be inserted at a time of an exhaust gas sampling inspection in a space between the tail pipe and the tale cover.
When exhaust is done by the muffler of such a constitution, pressure fluctuation occurs in the above-described gap, and concurrently therewith, air in the above-described space communicated with the cap vibrates, sometimes generating an abnormal noise called a “whistling sound”. In order to suppress an occurrence of such an abnormal noise, Patent Literature 1 discloses a technique to form a discharge port end portion of the tail pipe in a manner so enlarge an inside diameter toward the outside gradually or steppedly.    [Patent Literature 1] Japanese Laid-open Patent Publication 2001-182522
However, by only performing a processing described above to the tail pipe, it is difficult to sufficiently suppress the vibration of the air occurring in the space between the tail pipe and the tail cover, and a suppressing effect of the abnormal noise occurrence is limited.
Though narrowing the gap between the tail cover and the tail pipe enables prevention of the abnormal noise occurrence, in such a case it is hard to insert a tube in the above-described gap at a time of the exhaust gas sampling inspection, and the exhaust gas sampling inspection becomes troublesome. Further, extending the tail pipe more rear than the tail cover similarly enables prevention of the occurrence of the abnormal noise, but in such a case the rear end portion of the tail pipe is exposed from the tail cover, unsatisfying demand of design.